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Freeform Analogue Technologies PCP330

Procoder (FAT) By Chris Carter
Published November 1997

Following on from their Freebass TB303 clone, FAT's new PCP Procoder is another take on a classic instrument of the past — that mainstay of many a disco, electro, and Kraftwerk track, the analogue vocoder. Chris Carter absolutely refuses to make silly robot voices with it.

The FAT Procoder PCP330 is a new dedicated 1U rack vocoder from the same stable as the Freebass TB303 clone (/ The PCP330, however, is an all‑analogue device, with no MIDI or digital capabilities. The technical spec, while not on a par with top‑end models, is nevertheless pretty impressive; it employs an 11‑band voicing system that can also be pushed into service as a filter bank. In keeping with the analogue philosophy, there are separate controls for each function; a total of 19 knobs on the front panel. Eleven of these knobs are vocoder/filter level controls, and the rest are for adjusting the input and output levels, and the Sibilance and internal oscillator settings (of which more in a moment). To keep the audio signal as clean as possible, the Procoder also features a couple of peak‑reading LEDs, a compressor on the inputs to help prevent overdrive, and a noise gate on the outputs to keep the noise floor low.

Interfacing with the outside world is handled by four quarter‑inch jack sockets, and an XLR microphone input on the rear panel. The labelling for these rear‑panel sockets is confusing, as it doesn't relate to the terms normally employed in vocoding, or indeed to the labelling used on the front panel of the Procoder, as we shall see! From left to right, the connections are as follows: the Unvoiced In jack, the mono vocoder Out jack, the Synthese In jack, and finally, the two Analyse In sockets, one of which is a quarter‑inch line‑level jack, while the other is the mic‑level XLR. To understand the function of these connections, it's first necessary to know a little bit about how a vocoder works.

Theory & Operation

At its most basic, vocoding is a little like ring modulation, in that the vocoder takes two different input signals (known technically as the Carrier and the Modulator) and makes a third signal that is derived from combining the two. This is done by analysing the input sources, and using analysis and synthesis circuits to control banks of filters and VCAs (11 of each, in the Procoder's case). The effect of this is to superimpose the characteristics of the Modulator signal (usually, although not always, a voice, hence the term vocoder) over the Carrier (which is usually an instrument). If you use a voice as the Modulator and a synth note as the Carrier respectively, the end result is the instantly recognisable 'robot voice' vocoder effect; with a voice (Modulator) and a guitar (Carrier), you can create 'talking guitar' effects (for more on the theory behind vocoders, see the article all about them back in SOS January '94).

Getting the Procoder up and running is pretty painless, partly because it has an internal sawtooth oscillator (or sawtoot, as the manual insists on calling it); this acts as the Carrier signal so that you don't have to supply one if you don't want to. The oscillator is a basic affair, with a range from 15Hz to 600Hz (set using the front‑panel VCO Frequency control). Although it's referred to as a VCO, the oscillator can only be swept manually, and can't be controlled by an external control voltage keyboard signal or an LFO, which is a shame. However, the oscillator means that all you need to do to generate a vocoded sound is supply a Modulator signal, which is done via one of the Analyse In sockets on the back panel (XLR or jack, depending on whether your chosen Modulator is a mic‑ or line‑level signal). If you wish, you can also supply your own Carrier signal, and this is done via the Synthese In jack (plugging anything into this jack automatically disables the internal oscillator).

As already noted, the labelling for these jacks is misleading — one wonders why they couldn't have been labelled Modulator In and Carrier In, particularly as the relevant level controls on the Procoder's front panel are labelled Modulator and Carrier (the same dual terminology persists in the manual, incidentally). Anyway, if the front‑panel Modulator and Carrier level controls are set approximately mid‑way, and all the vocoder and filter level controls are set to maximum (which I suppose could be regarded as a default setting), all you need to do to obtain the familiar vocoder sound is plug a signal into one of the Analyse In jacks, use the internal oscillator as a Carrier, and bingo — the vocoder sound emerges from the Out jack on the rear panel. The vocoding theory might sound complex, but obtaining the sound is a doddle. There is an irritating hindrance, however; there are no graduations marked around the control knobs, which makes it very difficult to make a note of any particularly good settings you come across.

The only control I haven't explained so far is the Sibilance level knob. This controls a sub‑section of the vocoder called the VUD or the Voiced‑Unvoiced Detector, which is used to detect any sibilant content in the Modulator signal (the one from the mic/line input). If the circuit finds any, it superimposes a non‑harmonic noise signal over the harmonic vocoder sound. This feature would normally be used with a microphone and voice, and in this case, it adds intelligibility to the vocoded vocal. However, it works just as well (even better, some might say) with non‑vocal sources, particularly rhythmic sounds. Unusually, the VUD also allows for the internal noise generator to be overridden by yet another external audio source, which comes in via the Unvoiced In jack on the rear panel; so the PCP330 is actually a vocoder with the potential for three audio inputs. This certainly opens up even more creative sound‑shaping avenues, and might well be unique. Of course, getting the PCP330 to produce decent sounds depends a lot on the input material you choose. You can't expect to get those more unusual and wacky sounds straight away; you need to spend some time experimenting.

The Fun Part

I've always thought vocoders sound a lot more interesting when the Modulator signal is not a vocal signal, as this simply produces that totally clichéd voice box sound. I may be in a minority here, especially considering the current vogue for '70s sounds, but I stuck to my guns, and for this review, I only used a mic a couple of times to supply a vocal Modulator — and that was just to check that the XLR mic input socket worked as it should. It does, and there's plenty of gain available, if needed, via the Modulator Input Level control on the front panel.

During the course of the review, I used almost anything that had an output signal to drive the various vocoder inputs, including the following: a digital synth, an analogue synth, a Roland TB303 Bassline, a drum machine, drum pads, fuzz guitar, samples and sample loops, an effects unit, a radio, a TV and a PC soundcard. The fun part is trying out the various combinations of these, which often result in some unexpected results and happy accidents. An interesting input combination I came up with was feeding a TB303 through the Modulator (Analyse) input, an evolving synth pad through the Carrier (Synthese) input, and a hi‑hat pattern through the Unvoiced input. By adjusting the Sibilance level (which behaves a bit like a frequency‑dependent noise gate) it was possible to go from a smoothly changing, vocoded bubbly bass sound, to a chopped‑up, hard‑edged rhythm (although I discovered this effect by accident, it is described in the manual as a way of 'rhythmatising [sic] a static sound'). And by adjusting any of the 11 filter levels, it was possible to reduce or accentuate the bass, mid or top‑end ranges of the overall sound.

Although the PCP330 includes a compressor to reduce the likelihood of overloading the inputs, I still found it quite easy to push the vocoder into distortion, but because this is an analogue unit, this isn't an entirely unpleasant experience, and I can imagine some people using this feature to produce some suitably grungy lo‑fi vocoder sounds.

The Procoder manual contains some useful instructions on how to configure the vocoder to produce other non‑vocoder effects, including various types of pseudo‑filter sweeps, the 'rhythmatising' effect mentioned above, and frequency‑dependent distortion. This last effect works by feeding the same signal into both the Analyse and Synthese inputs; you can then tune the distortion across different frequency bands by adjusting the individual filter levels.

Strike Up The Bands

A few years ago, I used to have a Roland SVC350 vocoder, which was also an 11‑band unit, and I currently use the vocoder on the Korg Wavestation AD, which only has about six or seven bands. While the Roland unit sounded very warm, and the Korg sounds clean, neither have the strong, vibrant tones of the PCP330. The Procoder's output mixing options are also comprehensive, with level controls for the Carrier, Modulator, VCO, overall vocoder output and the filters, which allow for some complex layering of timbres. The Procoder can also pack quite a punch at the bottom end when processing drum loops and bass lines; just occasionally, it can sound a little too resonant in the mid section, although this can be eliminated with careful tuning. But beware of introducing the Sibilance (Unvoiced) effect too quickly, as it can change your sound quite alarmingly from a gentle chorus‑like effect to a loud 'sandpaper scratch' very rapidly.

They Don't Build 'Em Like They Used To

Though there's no denying that the PCP330 sounds great, as far as build quality goes, it's a bit of a duffer. As soon as I unpacked it, I knew something wasn't right — for a start, the top and bottom plates of the case aren't fixed to the frame, but sit loosely in grooves and rattle about, especially if you put the Procoder anywhere near a loud monitor or bass bin. There's also sharp, unfinished burring on the edges of the aluminium front panel, giving the overall impression of a Maplin self‑assembly kit. Furthermore, from a practical standpoint, I know FAT are trying to recreate a '70s look, with suitably blocky lettering in shocking pink, but if you view the unit from the wrong angle, or in anything other than bright light, the legending is almost illegible. You just don't get a feeling of pro‑quality construction from the PCP330, which is a bit ironic for a unit called a Procoder!


As I've said, the PCP330's sound is particularly strong, and the device offers more than enough controls to shape and tweak the sound (although the lack of graduations on the control knobs is a problem). Also, it does make a change to see a manufacturer coming up with something a little different, instead of cloning the same old bass synths, drum machines and filters. But I have to say that I think the £299 price is on the high side, particularly as there's no MIDI, CV or footswitch control. Couple this with my reservations about the build quality, and I'm afraid I can't recommend the PCP330 as wholeheartedly as I would have liked to. FAT do need to pay some attention to their quality control with regards to the Procoder's casing, because (to adopt a metaphor) it doesn't matter how good the engine is if the bodywork is in poor condition. Taken as a whole, it looks like FAT have cut too many corners with the PCP330; it just doesn't come across as good value for money. All I can say is try one before you part with your cash.


  • Versatile and easy to use.
  • Capable of producing some great sounds, with the right source material.
  • Good audio quality; even the distortion sounds OK!
  • A separate control for everything.
  • XLR socket for mic input as well as jack.
  • Built‑in oscillator.
  • Three independent audio inputs.


  • No on/off switch.
  • No footswitch socket.
  • Poor build quality.
  • The styling actually makes the legending impossible to read in some lighting conditions.
  • No graduations on knobs.
  • No external CV input for internal oscillator.
  • Expensive considering there's no MIDI, CV or footswitch control.


The PCP330 is a versatile, great‑sounding machine, capable of producing some extraordinary and unusual effects, and is only let down by its poor build quality and price. Try before you buy.